The present invention relates to a process for producing a semiconductor device and, more particularly, relates to a process for producing a semiconductor device which realizes excellent chip alignment to thereby enable improving a pickup efficiency.
Further, the present invention relates to a process for producing a semiconductor device and, more particularly, relates to a process for producing a semiconductor device in which not only can an appropriate amount of adhesive layer be easily formed on the back of extremely thin chips to thereby enable avoiding chip breakage, chip cracking or package cracking but also excellent chip alignment can be realized, so that a productivity enhancement can be realized.
In recent years, the spread of IC cards has been promoted, and further reduction of the thickness thereof is now demanded. Accordingly, it is now required that the thickness of semiconductor chips, which has been about 350 xcexcm, be reduced to 50-100 xcexcm or less.
Such thin semiconductor chips can be obtained by first sticking a surface protective sheet to a circuit surface of a wafer, subsequently grinding the wafer back and thereafter dicing the wafer. When the thickness of the wafer after the grinding is extremely small, chip breakage and chip cracking are likely to occur at the time of the dicing of the wafer.
As another means for attaining the reduction of the chip thickness, Japanese Patent Laid-open Publication No. 5(1993)-335411 discloses a process for producing semiconductor chips, in which grooves of given depth are formed from a wafer surface and thereafter the back of the wafer is ground. Further, this publication discloses a method in which, after the step of grinding the wafer back, pellets (chips) adhering to a mounting tape are detached (picked up) from the mounting tape and secured to a lead frame.
In this method, misregistration of chips adhering to the mounting tape may occur to thereby cause a pickup apparatus to suffer recognition failure with the result that a production efficiency would be lowered.
When it is intended to pick up semiconductor chips stuck to a mounting tape and secure the picked semiconductor chips onto a substrate, it is common practice to employ the method known as xe2x80x9cdispenser methodxe2x80x9d or the method in which a film adhesive is used.
In the dispenser method, a given amount of liquid adhesive is applied to sites of a substrate predetermined for securing semiconductor chips with the use of a dispenser, followed by press-bonding/fixing of semiconductor chips thereonto. However, this disperser method has drawbacks in that controlling the discharge amount of adhesive is difficult to thereby cause the adhesive amount to fluctuate, bringing about a variation of quality, and in that bleeding phenomenon occurs because the adhesive is liquid. When bleeding of the adhesive occurs, the adhesive may curl up to the upper surface of the chips, or the semiconductor chips may be inclined, so that failure is likely to occur at the time of wire bonding. Moreover, when packages, after resin sealing, are placed in high-temperature conditions, package cracking may be caused by volatile components which evaporate from any bled adhesive.
In the method in which a film adhesive is used, a film adhesive cut into substantially the same shape as that of the chip is adhered to sites of a substrate predetermined for fixing semiconductor chips in advance, or a film adhesive cut into substantially the same shape as that of the chip is adhered to chips, and the chips are fixed through the film adhesive to the substrate. However, in this method, it is required to cut the film adhesive into substantially the same shape as that of the chip in advance, so that practicing the method is time-consuming. Further, the work for adhering the film adhesive of the same extremely small size as that of the chip is requisite, so that the method is very laborious.
Even if any of the above means is employed, minute chips which have been ground to an extremely small thickness to thereby become very brittle are handled, so that chip breakage is likely to result from slight misoperation.
Therefore, there is a demand for the development of a method of easily and securely forming an adhesive layer on, especially, the back of chips.
With the intent to attain this task, the inventors, in Japanese Patent Application No. 11(1999)-340334, proposed xe2x80x9ca process for producing a semiconductor device, comprising the steps of:
providing a wafer of given thickness having a surface furnished with semiconductor circuits and a back;
forming grooves of a cut depth smaller than the thickness of the wafer, the grooves extending from the wafer circuit surface;
sticking a surface protective sheet onto the wafer circuit surface;
grinding the back of the wafer so that the thickness of the wafer is reduced to thereby finally result in division of the wafer into individual chips with spaces therebetween;
sticking a dicing/die bond sheet onto the ground back of the wafer, the dicing/die bond sheet comprising a base and, superimposed thereon, an adhesive layer, the sticking performed so that the adhesive layer is brought into contact with the ground back of the wafer;
peeling the surface protective sheet from the wafer circuit surface to thereby cause the adhesive layer of the dicing/die bond sheet to be exposed through each space between neighboring individual chips;
cutting the exposed adhesive layer of the dicing/die bond sheet;
detaching the individual chips having the cut adhesive layer adhering thereto from the base of the dicing/die bond sheet; and
bonding the individual chips through the adhesive layer to a given substrate.xe2x80x9d
This process enables easily and securely forming an appropriate amount of adhesive layer on the back of extremely thin chips.
However, when, after the sticking of the dicing/die bond sheet, the surface protective sheet is peeled, it may occur that the adhesive layer of the dicing/die bond sheet suffer strain to thereby result in misregistration of chips. Further, at the time of cutting of the adhesive layer, exposed between neighboring chips, of the dicing/die bond sheet, misregistration of chips may be caused by any vibration or flow of the adhesive layer. The misregistration of chips may cause a pickup apparatus to suffer recognition failure with the result that a production efficiency would be lowered.
The present invention has been made in view of the above state of the prior art. Therefore, it is an object of the present invention to provide a process for producing a semiconductor device which realizes excellent chip alignment to thereby enable improving a pickup efficiency. It is another object of the present invention to provide a process for producing a semiconductor device in which an appropriate amount of adhesive layer can easily be formed on the back of extremely thin chips to thereby enable avoiding chip breakage, chip cracking or package cracking, so that a productivity enhancement can be realized.
The first process for producing a semiconductor device according to the present invention comprises the steps of:
providing a wafer of given thickness having a surface furnished with semiconductor circuits and a back;
forming grooves of a cut depth smaller than the thickness of the wafer, the grooves extending from the wafer circuit surface;
sticking a surface protective sheet onto the wafer circuit surface;
grinding the back of the wafer so that the thickness of the wafer is reduced to thereby finally result in division of the wafer into individual chips with spaces therebetween;
sticking a pressure sensitive adhesive sheet for pickup step onto the ground back of the wafer, the pressure sensitive adhesive sheet for pickup step comprising a base and, superimposed thereon, an energy radiation curable pressure sensitive adhesive layer;
exposing the energy radiation curable pressure sensitive adhesive layer to an energy radiation; and
peeling the surface protective sheet from the wafer circuit surface.
In this first process, the energy radiation curable pressure sensitive adhesive layer of the pressure sensitive adhesive sheet for pickup step is cured prior to the peeling of the surface protective sheet. Therefore, even when the surface protective sheet is peeling, the cured pressure sensitive adhesive layer is free from strain, so that excellent chip alignment is realized to thereby enable improving a pickup efficiency.
The second process for producing a semiconductor device according to the present invention comprises the steps of:
providing a wafer of given thickness having a surface furnished with semiconductor circuits and a back;
forming grooves of a cut depth smaller than the thickness of the wafer, the grooves extending from the wafer circuit surface;
sticking a surface protective sheet onto the wafer circuit surface;
grinding the back of the wafer so that the thickness of the wafer is reduced to thereby finally result in division of the wafer into individual chips with spaces therebetween;
sticking a dicing/die bond sheet onto the ground back of the wafer, the dicing/die bond sheet comprising a base and, superimposed thereon, an adhesive layer;
performing a primary curing of the adhesive layer;
cutting the adhesive layer of the dicing/die bond sheet between neighboring individual chips;
detaching the individual chips having the cut adhesive layer adhering thereto from the base of the dicing/die bond sheet;
attaching the individual chips through the adhesive layer to a given substrate; and
performing a secondary curing of the adhesive layer to thereby secure the individual chips to the substrate.
The third process for producing a semiconductor device according to the present invention comprises the steps of:
providing a wafer of given thickness having a surface furnished with semiconductor circuits and a back;
forming grooves of a cut depth smaller than the thickness of the wafer, the grooves extending from the wafer circuit surface;
sticking a surface protective sheet onto the wafer circuit surface;
grinding the back of the wafer so that the thickness of the wafer is reduced to thereby finally result in division of the wafer into individual chips with spaces therebetween;
sticking a die bond sheet onto the ground back of the wafer, the die bond sheet comprising a base and, superimposed thereon, a thermoplastic adhesive layer;
cutting the thermoplastic adhesive layer of the die bond sheet between neighboring individual chips;
detaching the individual chips having the cut thermoplastic adhesive layer adhering thereto from the base of the die bond sheet;
attaching the individual chips through the thermoplastic adhesive layer to a given substrate; and
heating the thermoplastic adhesive layer to thereby secure the individual chips to the substrate.
In the present invention, when the surface protective sheet has an energy radiation curable pressure sensitive adhesive layer, it is preferred that the energy radiation curable pressure sensitive adhesive layer of the surface protective sheet be cured after the sticking of the surface protective sheet to the wafer circuit surface but before the grinding of the back of the wafer.
In these second and third processes of the present invention, because the fluidity of each of the adhesive layer of the dicing/die bond sheet and the adhesive layer of the die bond sheet is lowered at the time of peeling of the surface protective sheet, any strain of the adhesive layer would not be caused by the peeling of the surface protective sheet. Thus, excellent chip alignment can be realized to thereby enable improving a pickup efficiency. Moreover, in particular, misregistration of chips at the cutting of the adhesive layer can be avoided, so that chip recognition by a pickup apparatus can be performed accurately to thereby enable efficiently performing the production of semiconductor devices.